1. Field of the Invention
As magnetic recording technology continues to push areal recording density limits, magnetoresistive (MR) reproduce heads are the current technology of choice. Both shielded and unshielded MR heads are known in the art, and these heads have the advantage of high signal output level, independence of output level on head/media velocity, excellent short wavelength response and ease of fabrication. By use of electrodeposition techniques, mass production methods are being applied to MR head fabrication and large quantities of MR heads are manufactured using well known wafer processing techniques.
In the prior art, the necessary testing of these heads has proceeded at a slow pace. Generally, manual techniques are presently employed. To perform a test, a sense current through the test head's magnetoresistive strip is manually established. The head may be self biased by means of the sense current, or it may be biased by a deposited magnet incorporated into the head during the manufacturing process, or by other means known in the art. The head is then subjected to an excitation field directed along the response axis of the head, corresponding to the magnetic signal field read when the head is in use. Generally, in testing in the prior art, this field is generated by means of Helmholtz coils, and the magnitude of the field is calibrated in terms of the current flowing in the coils. Helmholtz coils provide accurately determinable fields but are limited to relatively low amplitude magnetic fields since the Helmholtz coil contains no high permeability pole pieces, but operates in empty space. In the prior art, the amplitude of the field at the head is generally determined by the calibrated current flowing in the Helmholtz coils, and the field level per reading is established by manual control of the current. With the field level established, a voltage measurement is made across the head's MR element, providing a data point for the manually set magnetic field and sense current. The efficiency of data collection in a manufacturing environment is limited by the low amplitude of magnetic field available from the Helmholtz coils, and the manual acquisition of the data on a point by point basis. The data is generally displayed in an analog graph form, and not being directly available for digital data processing typically results in derivation of qualitative rather than quantitative MR device parameters.